AIMS OF G ALACTIC C HEMICAL E VOLUTION STUDIES To check / constrain our understanding of stellar nucleosynthesis (i.e. stellar yields), either statistically (mean, dispersion) or in individual objects To establish a chronology of events in a given system e.g. when metallicity reached a given value, or when some stellar source (SNIa, AGB etc.) became important contributor to the abundance of a given isotope / element To infer how a system was formed (Star Formation Rate, large scale gas mouvements) e.g. slow infall of gas in case of solar neighborhood

THE SOLAR NEIGHBORHOOD SLOW INFALL (  = 7 Gyr) to fix G-dwarf problem, SNIa to account for [Fe/O] evolution PREDICTIONS : D evolution, evolution of abundances (depends on yields) AGE-METALLICITY METALLICITY DISTRIBUTION

Woosley and Weaver 1995, Overproduction factors of elements in massive stars

ABUNDANCES AT SOLAR SYSTEM FORMATION (Massive stars: Woosley+Weaver 1995; Intermediate mass stars: van den Hoek+Gronewegen 1997; SNIa: Iwamoto et al. 2000)

AGES OF GLOBULAR CLUSTERS AGES OF HALO STARS Marquez and Schuster 1994 Salaris and Weiss 2002

Norris and Ryan 1991

INFALL OUTFLOW

AGE – METALLICITY IN THE GALACTIC HALO Note: Instantaneous mixing approximation probably invalid at early times Stars of mass M > 2 Mʘ (Lifetime < 1 Gyr) enriched the Galaxy during the halo phase

NOTE: PRIMARIES VS SECONDARIES 1) CHEMICAL EVOLUTION (yield: IMF integrated or individual stars) PRIMARY: yield y P independent of Z SECONDARY: yield y S proportional to Z 2) STELLAR NUCLEOSYNTHESIS (yield from individual stars) PRIMARY: from H, He and their products (C,O) (yield not necessarily Z independent!) SECONDARY: from some metal at stellar formation (yield not necessarily proportional to Z!)

NITROGEN PRODUCTION MASSIVE STARS (  10 7 years): Secondary Non Rotating : INTERMEDIATE MASS (  10 8 years): Primary LOW MASS STARS (  10 9 years): Secondary Rotating: MASSIVE STARS (  10 7 years): Secondary Stars INTERMEDIATE AND LOW MASS (  10 8 years):  Primary STELLAR CNO YIELDS

C and N abundances always follow Fe PRIMARIES ? But:  2/3 of Fe in disk come late from SNIa ⇩  2/3 of C and N in disk come from a late source (not operating in halo)  Low mass stars ?  Secondary N (but C?)  Z-dependent yields from massive stars? No sign of secondary N in early halo: Which primary source? EVOLUTION OF CNO IN SOLAR NEIGHBORHOOD

Stellar rotation has similar effect on yields of nitrogen (mostly from Intermediate mass stars) as Hot Bottom Burning Difficult to explain earliest primary Nitrogen (Massive star yields insufficient -even with rotation…) However: timescales at low [Fe/H] uncertain ! Secondary N production at late times  matches Fe production from SNIa [N/Fe]  0 Not exactly the case for C…

FRACTIONAL CONTRIBUTION TO NITROGEN-14 PRODUCTION FRACTIONAL CONTRIBUTION TO CARBON-12 PRODUCTION

PRIMARY NITROGEN… WITH RESPECT TO WHAT ??? WW95 + VdHG97 MM02 No Rot MM02 + Rot PSEUDO-SECONDARY BEHAVIOUR WITH RESPECT TO OXYGEN

Inside-Out formation and radially varying SFR efficiency required to reproduce observed SFR, gas and colour profiles (Scalelengths: R B  4 kpc, R K  2.6 kpc) (Boissier and Prantzos 1999) THE MILKY WAY DISK

METALLICITY PROFILE OF MILKY WAY DISK Present day gradient : dlog(O/H)/dR ∼ dex/kpc Models predict (e.g. Hou et al ) that abundance gradients were steeper in the past

METALLICITY PROFILE OF MILKY WAY DISK Recent observations (Maciel et al 2002) of planetary nebulae of various ages support that prediction: The disk was formed inside-out “Observed” evolution of O gradient: d[dlog(O/H)/dR]/dt ∼ dex/kpc/Gyr In broad agreement with theory

ABUNDANCE GRADIENTS OF CNO IN MILKY WAY DISK O : dlog(O/H) / dR = dex/kpc But: Deharveng et al. (2001): dex/kpc N: dlog(N/H) / dR = dex/kpc C : dlog(C/H) / dR = dex/kpc

C and O not sensitive to different sets of yields (primaries) For N, stellar yields up to Z=3 Z ⊙ (not available at present) are required in order to model the inner disk ABUNDANCE GRADIENTS OF CNO IN MILKY WAY DISK